1. Field of the Invention
This invention lies within the field of seismic streamer cables for marine use and in particular relates to a means for interconnecting a plurality of sections to form a complete streamer cable.
2. Description of the Prior Art
In marine seismic surveys, a ship tows a neutrally buoyant streamer cable through the water along a line of survey. The complete streamer is composed of a plurality of separate active sections that are interconnected by suitable coupler sections. Typically each active section may be 200 to 300 feet long. Fifty or more such sections may be employed to make up the complete streamer which may be more than two miles long. When not deployed for use, the streamer cable is wound on a huge cable reel mounted on the stern of the ship.
Typically, each section consists of a hose-like cylindrical jacket of plastic such as polyvinyl chloride about 2.5 to 3.0 inches in outside diameter. A plurality of plastic spacers are disposed inside the jacket at desired intervals along the length of the section. Two or more steel stress members are threaded through holes around the periphery of the spacers to absorb the towing tension. A plurality of hydrophones are mounted inside the jacket at suitable locations between the spacers. A plurality of conductor pairs, for transmitting signals from the hydrophones to a recording device aboard the ship, are laced into a wire bundle that is threaded through central holes in the spacers. There may be 225 or more conductor pairs.
Each end of the section is sealed by a terminal bulkhead. The terminal bulkhead fits snugly inside the ends of the jacket. The jacket is then fastened tightly to the terminal bulkhead by metal bands to form a water-tight seal. After assembly, the cable section is filled with a low-specific-gravity kerosene through an oil-fill valve in the terminal bulkhead to render the section neutrally bouyant. The stress members protrude through the terminal bulkheads at each end of the section, extending one or two feet beyond the section ends. The stress members are terminated by aircraft-type clevises. The conductor pairs also extend through and beyond the terminal bulkhead. The conductor pairs are soldered to the terminals of miniature flat pin-and-socket connector plugs. Each plug may include about 25 contact pairs so that nine such plugs are needed for a 225-pair wire bundle. The plugs are staggered longitudinally with respect to each other over a distance of one to three feet beyond the ends of the section so that no two connector plugs abut one another. The holes through which the stress members and the wire bundle penetrate the terminal bulkheads are sealed so as to be watertight.
The structure of typical streamer cables are described in U.S. Pat. No. 2,465,696 to Paslay, U.S. Pat. No. 3,290,645 to Pavey, Jr. et al and U.S. Pat. No. 4,092,629 to Siems et al.
Various ways have been devised to connect two adjacent cable sections together. Commonly the mating stress-member clevises, from the two sections to be connected, are coupled together by suitable pins which are locked in place by cotter pins. The respective mating connector plugs are joined and locked in place. The combined lengths of the coupled protruding stress members associated with the two cable sections are adjusted so that the wire bundles are slack when the stress members are under tension. Upon completion of the mechanical and electrical connections a short protective boot, consisting of a length of plastic hose, is slipped over the exposed connector plugs and stress members. The boot, usually two to six feet long, is filled with kerosene for buoyancy and electrical insulation purposes. The boot is secured to the terminal bulkheads of the adjacent cable sections by metal bands thereby protecting the electrical connector plugs and stress members from water invasion. See particularly U.S. Pat. No. 3,376,948 to Morrow, FIGS. 1, 1a for an illustration of conventional couplers.
Despite its seeming simplicity, the coupler section above described is unsatisfactory for a number of reasons. The metal housings of the connector plugs, being necessarily in intimate contact with portions of the wire bundles, chafe the insulation of the conductors when the streamer cable is wound on or off the storage reel. Chafing causes short circuits and sometimes wire breakage. It is often necessary to disassemble the coupler sections in the field for repair. Disassembly is time-consuming and tedious because the metal bands must first be cut away, the kerosene poured out and the boot removed. Thereafter, the stress members must be disconnected. Reassembly is equally tedious. Additionally, since the coupler section is filled with kerosene, when the coupler section is disassembled the wires and plugs are oil-saturated, creating a messy work area and a potential fire hazard. Furthermore, a coupler section for use with streamer cables having 200-300 conductor pairs may be up to six feet long so that the connector plugs can be properly spaced apart. For a 50-section cable, the coupler sections add up to an extra 300 feet of cable that must be stored on the cable reel which has an inherently limited capacity.
There is a need therefore for a clean, more convenient, shorter coupler section that can be easily and quickly disassembled and reassembled in the field.